In general, in a vehicle such as a four-wheeled automobile, an air suspension system configured to adjust a vehicle height is mounted. The air suspension system includes an air suspension configured to adjust a vehicle height according to supply/discharge of air, a compressor configured to compress air to be supplied to the air suspension, and a high-pressure tank configured to store the air compressed by the compressor. In addition, the air suspension system is configured such that when the compressed air stored in the high-pressure tank is supplied to the air suspension, the vehicle height increases (see, for example, Patent Document 1).
Meanwhile, in the related art, in order to lower the vehicle height, air is discharged from the air suspension, and the discharged air is stored in a low-pressure tank. Then, the compressor compresses air having a pressure equal to or higher than an atmospheric pressure, which is stored in the low-pressure tank, and stores the compressed air in the high-pressure tank. Accordingly, a pressure difference between a suction side and a discharge side of the compressor may be suppressed, and the pressure when air is compressed by the compressor may be reduced.